Field of the Invention
The invention relates to a method for controlling a steam turbine with a steam bleed. The invention also relates to a control device for such a steam turbine.
A control of a steam turbine with bleed steam, called a bleeder turbine for short, is described in the book having the title xe2x80x9cRegelung von Dampfturbinenxe2x80x9d [xe2x80x9cClosed-loop control of steam turbinesxe2x80x9d] by Adolf Brxc3xccher, 2nd edition, 1972, Kraftwerkunion AG, Mxc3xclheim/Ruhr, from page 53 in the Chapter xe2x80x9cReglereinstellblatt bei gesteuerten Entnahmeturbinenxe2x80x9d [xe2x80x9cRegulator adjustment sheet for controlled bleeder turbinesxe2x80x9d]. In the case of a bleeder turbine, steam for normal operational purposes is bled off from a specific stage. If steam is bled off to condensation or feed-water preheaters, only one connection is provided from the stage to these preheaters, without any closed-loop control element. This is a so-called uncontrolled bleeding or tapping. The pressure at a tap is governed by the flow rate or amount of the steam passing through the turbine.
In contrast to this, it may be necessary to provide steam at a specific pressure, irrespective of the magnitude of the turbine steam flow rate, and thus the electrical power. However, this requirement can be satisfied only if it is possible to maintain pressure. In this case, the steam turbine is a controlled bleeder turbine. For example, steam flows into the high-pressure section of such a bleeder turbine. At the end of the high-pressure section, the steam flows on the one hand into a steam bleed line, and on the other hand into a low-pressure section of the turbine. The steam which flows through the low-pressure section can then be supplied not only to a condenser but also, once again, to a bleed line. The latter configuration is referred to as a backpressure bleeder turbine. Thus, the function of a bleeder turbine is not only to drive a generator, but also to provide so-called process steam for operational purposes.
Depending on the desired amount of electrical power or the desired amount of process steam, different operational tasks arise with regard to the closed-loop control of the bleeder turbine. These tasks are characterized by different types of controlled variables that are used for closed-loop control. The controlled variables may be, for example, a bleed steam flow rate, a power level emitted from the turbine, a rotation speed of the turbine shaft, a backpressure in the steam flowing out of the turbine, or an initial pressure in the steam flowing into the turbine. One operational task would thus be characterized, for example, by closed-loop control on the basis of the bleed steam flow rate and the power. Another operational task would be characterized, for example, by closed-loop control on the basis of the bleed steam flow rate and the backpressure.
U.S. Pat. No. 4,146,270 discloses a control device for a steam turbine with speed and power control coupled on the output side. A fuzzy controller described in the article xe2x80x9cDampfturbinenregelung mit Fuzzy-Logikxe2x80x9d [steam turbine regulation with fuzzy logic], R. Hampel, N. Chaker, in ATP Automatisierungstechnische Praxis [automation engineering in practice], 37 (1995), June, No. 6, Munich, Germany, is intended to permit such regulation in the case of a steam turbine with steam bypass stations. Nevertheless, until now, a specific control structure has been used for each operational task. Parameters obtained empirically are in this case linked so that the desired control response is obtained for the operational task. Both the parameters and the linking of the parameters thus differ from one another, so that use is always made of different control structures.
It is accordingly an object of the invention to provide a method for controlling a steam turbine with a steam bleed which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which is matched in a simple and operationally reliable manner to the operational tasks of the steam turbine. It is a further object of the invention to provide a control device for a steam turbine with a steam bleed that carries out the operational tasks of the steam turbine in a simple and operationally reliable manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling a steam turbine, the method includes the steps of:
regulating a steam feed via a feed valve, and regulating a steam bleed via a bleed valve;
supplying, with a first regulator or a second regulator, a first control signal and a second control signal to a regulating structure as a function of controlled variables fed to the first regulator or the second regulator;
linking, when there is a task-specific change between the first and second regulators, by using always a same regulating structure including a parameter set subdivided into subgroups, each subgroup having a first parameter and a second parameter, a result of a conversion of the first control signal with the second parameter and a result of a conversion of the second control signal with the first parameters to one another;
determining a first actuating signal with a first one of the subgroups and determining a second actuating signal with a second one of the subgroups; and
feeding the first actuating signal to the feed valve and feeding the second actuating signal to the bleed valve.
In other words, a method for controlling a steam turbine is provided in which a steam feed is regulated via a feed valve and a steam bleed is regulated via a bleed valve, wherein a first regulator or a second regulator emits a first control signal and a second control signal to a regulating structure as a function of the controlled variables respectively fed to them, wherein, during a task-specific change between the regulators by using a regulating structure which is always the same and has a parameter set subdivided into subgroups each having a first parameter and a second parameter, within each subgroup, the result of a conversion of the first control signal using the second parameter and the result of a conversion of the second closed-loop control signal using the first parameters are linked to each other, and wherein a first actuating signal fed to the feed valve is determined with a first subgroup, and a second actuating signal fed to the bleed valve is determined with a second subgroup.
There may also be a plurality of feed valves or else a plurality of bleed valves, and corresponding regulators. A bleed valve may also at the same time be a feed valve. For example, a steam bleed from a first stage of the steam turbine may be controlled by adjusting a feed steam quantity or flow rate (feed flow rate for short) for a second stage in the steam turbine, following the first stage, such that the desired bleed steam quantity or flow rate (bleed flow rate for short) is obtained from the difference between the respective feed flow rate supplied to the first stage and that supplied to the second stage.
A steam feed or else a steam bleed may be supplied to or taken from any point on the steam turbine, depending on the requirement. The operational tasks are characterized by the nature of the controlled variables, depending on the desired emission of power from the turbine or the desired bleed steam flow rate. For example, one operational task is characterized by a (closed-loop) control based on the steam bleed flow rate the rotational speed of the turbine.
The control structure is used to convert the control signals from the regulators into actuating signals for actuating elements for the feed or bleed valve. Depending on the operational task, this conversion must be carried out in a manner matched to the operational task, since each operational task is based on a different operating envelope for the feed or bleed valve.
In the invention only a single control structure is now used for this purpose for all the operational tasks. In this case, each operational task is now in each case characterized only by a specific set of parameters for the common control structure. The entire control system for the steam turbine is thus simplified. Furthermore, a high level of operational reliability is ensured since a smooth changeover can be carried out by the same control structure, in particular when changing from a first to a second operational task. This means that there is no sudden change to the actuated actuating element when changing from a first regulator to a second regulator. Such a sudden change in an actuating element position, which until now could not be ensured, since different control structures were used for the various tasks, results in a high mechanical load on this actuating element.
The common control structure for all the operational tasks means that it is possible to ensure that the controlled variables are largely decoupled from one another. This means that, for example, there is no significant change in power from the steam turbine when a change is made to the bleed steam flow rate. The desired parameters can thus be set independently of one another, depending on the operational requirement. With a control with different regulator structures for each operational task by empirically obtained parameters, such decoupling over the entire operating envelope is virtually impossible, due to the large number of parameters. In contrast, with the common control structure, the control structure parameters for the respective operational task are defined in a simple manner, using coupling functions between the controlled variables, such that the controlled variables are decoupled from one another. The parameters are preferably furthermore defined such that an operating envelope is defined which is matched to the chosen operational task.
One of the controlled variables is preferably a bleed steam amount or flow rate, a pressure in the steam turbine, a power level of the steam turbine, or a rotational speed of the steam turbine.
Each operational task is assigned a parameter group, which characterizes it, for the control structure. When a change is made from a first of the operational tasks to a second of the operational tasks, a change takes place from a first regulator to a second regulator such that initial variables for the output of the second regulator are fixed through the use of an inverse closed-loop control structure. The inverse closed-loop control structure is in this case the inverse of the closed-loop control structure with the parameter group for the second operational task. The initial variables are supplied to the second regulator. The second regulator thus starts with values which correspond to the last actuation of the first regulator from the old operational task. This means that there is no sudden change to the actuation of the actuating element. The initial variables for the second regulator are defined in a simple manner by using the common control structure in such a way that the initial variables are recalculated through the use of the inverse control structure from the actuating variables of the first regulator. The inverse control structure corresponds to reverse calculation of the control structure, with the control structure parameters being used as the basis for the new operational task. A smooth changeover between operational tasks is thus achieved in a simple manner.
Each parameter group preferably includes a feed valve subgroup and a bleed valve subgroup, in which case a first one of the control signals is linked to a first parameter, and a second one of the control signals is linked to a second parameter of each of these subgroups, and in which case the feed valve manipulated variable and the bleed valve manipulated variable, respectively, are additionally determined through the use of a respective offset parameter associated with each subgroup.
With the objects of the invention in view there is also provided, a control device for a steam turbine, including:
two regulators;
the two regulators receiving respective controlled variables and the two regulators respectively outputting, as a function of the controlled variables a first control signal and a second control signal;
a regulating structure receiving the first control signal and the second control signal, the regulating structure being a same regulating structure for the two regulators; and
the regulating structure including a parameter set subdivided into subgroups, each of the subgroups having a first parameter and a second parameter, the regulating structure linking a result of a conversion of the first control signal with the second parameter and a result of a conversion of the second control signal with the first parameters to one another such that a first one of the subgroups generates a first actuating signal for a feed valve, and a second one of the subgroups generates a second actuating signal for a bleed valve.
In other words, a control device for a steam turbine with two regulators which, as a function of controlled variables fed to them in each case, emit a first control signal and a second control signal to a control structure that is the same in both regulators, wherein the control structure having a parameter set subdivided into subgroups, each having a first parameter and a second parameter within each subgroup, links the result of a conversion of the first control signal with the second parameter and the result of a conversion of the second control signal with the first parameters to one another, and wherein a first subgroup generates a first actuating signal for the feed valve, and a second subgroup generates a second actuating signal for the bleed valve.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for closed-loop control of a steam turbine with a steam bleed, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.